Can't she leave the dogs at home, or in her car? After all, it is your cat's home & she must feel really put out by this. Having said that, my cats would just beat up any strange dog who dared to set foot over our threshold!! It has been known...
Both cats and dogs are territorial animals, and your cat will be giving off territorial signals to which the dogs respond.
It's nature, and despite your best intentions, you won;t change it.
Frankly, your friend should have noted this reaction the first time she visited, and made arrangements for her dogs at all subsequent times - as advised, it is unfair on your cat.
if they lived together they would be fine but i can't see them getting on when introdced to each other infrequently. The others are correct in saying the dogs should be left at home or if you have requested to see the dogs you could put the cat in another room or outside for the duration of the visit.